Simplifying Backscatter Deployment: Full-Duplex LoRa Backscatter

Due to the practical challenges in the deployment of existing half-duplex systems, the promise of ubiquitous backscatter connectivity has eluded us. To address this, we design the first long-range full-duplex LoRa backscatter reader. We leverage existing LoRa chipsets as transceivers and use a microcontroller in combination with inexpensive passive elements including a hybrid coupler, inductors, tunable capacitors, and resistors to achieve 78 dB of self-interference cancellation and build a low-cost, long-range, and small-form-factor Full-Duplex LoRa Backscatter reader.

We evaluate our system in various deployments and show that we can successfully communicate with a backscatter tag at distances of up to 300 ft in line of sight, and through obstacles, such as walls and cubicles, in a 4,000 ft 2 office area. We reconfigure our reader to conform to the size and power requirements of a smartphone, and demonstrate communication with a contact-lens-form-factor prototype device. Finally, we attach our reader to a drone and demonstrate backscatter sensing for precision agriculture with an instantaneous coverage of 7,850 ft 2 . * Work was done while the author was at Jeeva Wireless. 1 active RFIDs are also radios 100 meters separation 30 dBm -50 dBm -134 dBm LoRa Tag Carrier Source Receiver (a) Half-Duplex deployment. The carrier source and receiver are separated by 100m to mitigate carrier interference. 30 dBm -134 dBm CW Carrier LoRa Backscatter packet Co-located Carrier Source and Receiver LoRa Tag (b) Full-Duplex deployment. The carrier source and receiver are co-located and need 78 dB interference cancellation.